1. Field of the Invention
The present invention relates to a scanning apparatus for an original image.
2. Description of the Prior Art
In a prior art copying machine capable of copying only at an equi-magnification, a position detector for determining a reversal point in accordance with the size of a copy sheet is provided in an optical system which scans a movable optical system in order to determine a scan length for an original. For example, reversal point detectors for copy sheet sizes of B5, A4, B4 and A3 are provided in the optical system, and when an A4 cassette is loaded in the copying machine, the optical system is reversed when it reaches the size A4 reversal point detector. In a copying machine with variable magnification copy function, it is usual that the copying is allowed at only a predetermined magnification factor such as from the size A3 to the size B4 or from the size A3 to the size A4. Accordingly, the scan length of the optical system can be relatively simply determined. For example, when the magnification factor is a reduction from the size A3 to the size B4, the scan length of the optical system is controlled by the size A3 reversal point detector.
In a copying machine having a multi-step variable magnification copy function, it is very complex to determine the scan length of the optical system because the magnification factor may be set to any desired length.
In a simple method, a maximum scan length is used without regard to the magnification factor and the copy sheet size. However, it is not practical because of low copying speed.
In the copying machine with continuously variable magnification copy function, it is difficult to synchronize the speed of a reciprocating means such as the optical system or original mount table with an overall speed of the copying machine because the speed of the reciprocating means is continuously variably changed.
A separate high speed motor may be used to return the scanner after the completion of scan, but it leads to increased cost.
When the multi-step variable scale copy function is used, an operator may not know what magnification factor is actually selected.